Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

2. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

One heat exchanger

Three heat exchangers

3. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Large latent heat

Low boiling point

Good electrical conductor

4. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

At critical Temperature

5. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Rankine

Reversed Rankine

Carnot

6. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

7. The capillary tube, as an expansion device, is used in

Room air conditioners

Domestic refrigerators

Water coolers

All of these

8. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

2.33

1.33

3.33

9. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Collect vapours

Superheat the vapour

10. Rating of a domestic refrigerator is of the order of

40 tons

10 tons

5 tons

0.1 ton

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11. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

12. The boiling point of ammonia is

-33.3°C

-77.7°C

-10.5°C

-30°C

13. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

14. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Compressor and condenser

Condenser and receiver

Receiver and evaporator

15. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

16. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Always less than unity

Always more than unity

Equal to unity

17. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Freon

Ammonia

Brine

18. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Miniature sealed unit

Axial

Centrifugal

19. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-77.7°C

-56.6°C

20. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

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21. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

22. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant temperature

Takes place at constant entropy

Takes place at constant pressure

23. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

24. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

9: 1

1: 9

25. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.6

0.376

0.67

26. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

27. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

None of the above

28. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

29. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

30. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

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31. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

2 bar

30 bar

32. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

33. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Zero

Positive

34. For obtaining high COP, the pressure range of compressor should be

Any value

High

Optimum

Low

35. Freon group of refrigerants are

Inflammable

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

36. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

37. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Stirling

Ericson

Carnot

38. Most thermostatic expansion valves are set for a superheat of

10°C

5°C

20°C

15°C

39. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

40. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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